Vaccines

Summary

Vaccines help reduce the risk of certain infectious diseases by introducing dead or weakened versions of disease-causing germs (bacteria or viruses) to the immune system.

Some vaccines offer lifelong immunity.

Immunisation greatly reduces the risk of catching a disease, which in turn reduces the risk of complications.

Vaccines trick the body into building immunity against infectious diseases without causing the actual disease. Vaccines achieve this by introducing a dead or weakened version of the disease-causing germ (bacteria or virus) to the body’s immune system. In some cases, inactivated toxins (poisonous substances) produced by the germ are used in the vaccine to develop immunity (for example, diphtheria and tetanus vaccines).

After vaccination, if our immune system encounters the ‘real’ disease-causing germ, quick recognition allows our body to fight infection or neutralise toxins with a rapid and effective immune response.

Immunisation (vaccination) is the most effective preventative measure against infectious diseases. Some vaccines offer lifelong immunity. In other cases, booster shots are needed.

Serious side effects from vaccines are rare and much less common than the serious effects of the disease. Some diseases, such as poliomyelitis or diphtheria, can be so serious that the infected person may suffer lifelong complications or even die.

How vaccines work

The human immune system is made up of special cells and chemicals that fight infection. The human body can gain immunity against certain diseases either naturally (by catching and surviving or coming into contact with the illness) or through immunisation.

Vaccines work by introducing a modified version of a disease-causing germ or toxin to the immune system. People are usually given an injection or a small drink (that contains the vaccine). Depending on the disease, the vaccine could be a weakened or dead germ, or a part of the germ (for example, a molecule from the surface of the germ). In other cases, toxins (poisonous substances) produced by bacteria cause the disease and so the vaccine will contain an inactivated toxin.

The immune system responds to the weakened, partial or dead germ or inactivated toxin as if it was a fully-fledged germ and makes antibodies to destroy it. These antibodies are made without the person getting sick.

Later, some of these antibodies remain ‘on patrol’ in the bloodstream and the immune system can quickly produce more antibodies if it encounters the actual germ. This means that the key to defeating that particular disease is stored in the immune system long term (known as immunological memory).

Vaccines stimulate immunity against disease

A person’s immune system is like a library that contains information about every germ ever defeated. If the person encounters the real disease-causing germ in the future, their immune system will know how to defeat it, often before the person experiences any symptoms of illness. This explains why (in most cases) you only catch diseases such as mumps and rubella (German measles) once, even though exposure to the viruses may be repeated throughout life.

Each vaccine is designed according to how the specific germs make you sick. For example, measles is the result of the body’s reaction to the whole virus and so the vaccine contains a weakened form of the virus. On the other hand, tetanus is caused by the body’s reaction to the toxin produced by the tetanus bacteria and so the vaccine contains inactivated tetanus toxin.

Immunisation and HALO

The immunisations you may need are decided by your health, age, lifestyle and occupation. Together, these factors are referred to as HALO.

HALO is defined as:

Health– some health conditions or factors may make you more vulnerable to vaccine-preventable diseases. For example, babies born prematurely, or people who have asthma, diabetes, heart, lung, spleen or kidney conditions, Down syndrome and human immunodeficiency virus may benefit from additional or more frequent immunisations.

Age – at different ages you need protection from different vaccine-preventable diseases. Australia’s National Immunisation Program sets out recommended immunisations for babies, children, older people and other people at risk, such as Aboriginal and Torres Strait Islander people. Most recommended vaccines are available at no cost to these groups.

Lifestyle – lifestyle choices can have an impact on your immunisation needs. If you are travelling overseas to certain locations, planning a family, are sexually active, smoke, or play contact sport that may expose you directly to someone else’s blood, you may benefit from additional or more frequent immunisations.

Occupation – you are likely to require additional or more frequent immunisations if you work in an occupation that exposes you to vaccine-preventable diseases, or puts you in contact with people who are more susceptible to problems from vaccine-preventable diseases such as babies or young children, pregnant women, the elderly, and people with chronic or acute health conditions. Workers in aged care, childcare, healthcare, emergency service, or sewerage repair and maintenance need to discuss their immunisation needs with their doctor. Some employers help with the cost of relevant vaccinations for their employees.

Talk to your doctor or immunisation provider if you think you or someone in your care has health, age, lifestyle or occupation factors that could mean immunisation is necessary. You can check your immunisation HALO using the downloadable poster (pdf).

History of immunisation

Immunisation techniques were pioneered over 200 years ago, when smallpox was a feared and deadly disease. An eighteenth century doctor named Edward Jenner noted that workers on farm who contracted the mild cowpox disease were immune to smallpox. Jenner guessed that the germ responsible for cowpox was similar enough to the smallpox germ to ‘train’ the immune system to defeat both diseases. He was correct. Immunisation today relies on similar principles.

No vaccine is completely effective

Out of 100 people immunised against a particular disease, about five to 15 will catch the disease if they are exposed to it. This may be because their immune systems didn’t respond to the vaccine and failed to make antibodies, or the vaccine may not have been stored correctly at the clinic.

However, if 100 people who have never had measles or never received the measles vaccine were exposed to the disease, almost every single one of them would catch it. Immunisation greatly reduces the risk of catching a disease, which in turn reduces the risk of complications.

Comparing the risks of vaccines

From time to time, the safety of vaccines has been questioned. Like any other medication, vaccines carry a small degree of risk, but serious side effects are very rare. The risk of serious side effects must be weighed against the risk of the disease. For example, the risk of encephalitis (inflammation of the brain) from the measles, mumps, rubella (MMR) vaccine is thought to be just one in a million immunisations. However, according to some estimates, the risk of encephalitis from catching the mumps virus is one in 200.

Immunisation success stories

Immunisation is the most effective preventative measure against infectious diseases. Some recent immunisation success stories in Victoria include:

Meningococcal C disease– from a peak of 88 cases in 2002, the number of cases has fallen every year since the introduction of meningococcal C vaccine in 2003. In 2015, there were no cases reported in Victoria. The last reported case was in 2013.

Haemophilus influenzae type b (Hib) disease – since immunisation against Hib disease was introduced in Victoria in 1993, cases among children under four years of age have dropped by more than 70 per cent in just one year. Since 2000, there has been an average of less than one case per year in this age group.

Measles – measles rates have been decreasing since 1969 when the vaccine became available in Australia. The most significant impacts have been from its inclusion on the National Immunisation Program in 1983, the introduction of a second measles vaccine dose in 1994 and a primary school Measles Control Campaign in 1998. In Victoria, the average number of measles cases decreased from 75 cases per year between 1997 and 1999 to an average of 24 cases per year between 2005 and 2015. The most common group of people seeking treatment for measles since 2000 (more than two-thirds of cases) are those who were born after 1966 (who were not exposed to the pre-vaccine era of large outbreaks) and people born before 1982 (who were not vaccinated or only received one dose). The majority of these people have contracted measles during overseas travel.

Australia’s National Immunisation Program

The National Immunisation Program sets out recommended immunisations for infants, children, older people and other people at risk, such as Aboriginal and Torres Strait Islander people. Most recommended vaccines are available at no cost to these groups. If you need further information, talk to your doctor.

Content Partner

This page has been produced in consultation with and approved by:
Department of Health and Human Services - RHP&R - Health Protection - Communicable Disease Prevention and Control Unit

Last updated:
December 2015

Page content currently being reviewed.

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.